The provision of tamper-indicating or tamper-evident closures for containers is desirable for all manner of consumer products, so that partial or complete removal of the closure results in clearly discernible visible alteration thereof. Typically, closures of this nature include an upper cap portion, and a depending pilfer band arranged to interact and cooperate with the container to which the closure is applied. The pilfer band is typically configured so as to fracture and/or separate from the closure cap attendant to closure removal, thereby providing clearly discernible evidence that the container has been opened.
Various techniques are known for effecting the desired interaction of a closure pilfer band with the associated container. For example, the pilfer band may be deformed after application to the container to achieve the desired interaction, such as is the case with so-called roll-on metallic closures. A similar interaction is achieved with so-called heat-shrink plastic closures, wherein the closure includes a heat-shrinkable pilfer band which is heat-shrunk into a configuration for tamper-indicating interaction with the container subsequent to application thereto. Other arrangements, such as disclosed in commonly-assigned U.S. Pat. No. 4,418,828, to Wilde et al., include pilfer bands having flexible elements which move to an out-of-the-way disposition during application of the closure to the container, with the flexible elements thereafter cooperating with the container to provide the desired tamper-indicating function.
Another type of tamper-indicating closure includes so-called interference-type pilfer bands. For use of such arrangements, the container includes an annular, bead-like external locking ring on the neck portion thereof, ordinarily positioned just beneath an external thread formation on the container neck. The pilfer band of the closure in turn includes a pilfer band having an internal ledge, lip, bead, or like projection or projections intended to cooperate with the container locking ring for tamper-indication. Specifically, the pilfer band is configured to move past and generally beneath the container locking ring during application of the closure to the container, with the inner projection of the pilfer band dimensioned so as to interferingly engage the container locking ring after the closure is fully fitted to the container. During removal, this mechanical interference between the pilfer band and the locking ring creates stress on the closure, which is typically configured for fracture of the pilfer band, and/or fracturable separation of the pilfer band from the upper cap portion of the closure.
Design of consistently reliable interference-type tamper-indicating closures can be problematical. As will be appreciated, it is of utmost importance that a tamper-indicating closure be capable of withstanding the stresses during application without failure (ordinarily during application by high-speed capping equipment), while at the same time fracturing in the intended manner reliably and predictably during closure removal. These ends must be achieved while recognizing that both closures and containers are subject to normal manufacturing tolerances, which can, of course, result in a relatively "large" closure (within tolerances) being fitted to a relatively "small" container, or vice versa.
In the past, these design considerations have complicated development of effective interference-type closures. During application, the interfering element of the closure pilfer band, which is typically arranged perpendicularly to the axis of the closure, engages the container locking ring generally completely about the circumference of the closure. Since the closure must deform outwardly to clear and "snap over" the locking ring, relatively great force is required for application. The fracturable components of the closure are subjected to this stress, and must be capable of withstanding it without failure.
Proper function of the closure further requires that the fracturable components fracture reliably during closure removal. This can be difficult to achieve, since during removal, the typically perpendicular interference element of the pilfer band engages the container locking ring so that the stress that is generated is typically equally distributed about the circumference of the closure. Thus, this fracturing stress is generally equally distributed to fracturable elements or the like connecting the pilfer band and closure cap.
Since no one or group of such fracturable elements are preferentially stressed during removal, a relatively great interference force must be created to assure fracture. However, in a typical construction, the greater the interference, the greater the forces that are created during closure application, thus requiring stronger" fracturable components, which require greater interference stresses during removal, etc.
The present invention contemplates an interference-type tamper-indicating closure which is specifically configured to overcome these problems by deforming the pilfer band during closure application to minimize stresses which are created, and thereafter selectively and progressively stressing the fracturable components of the closure to provide consistent, reliable tamper-indication.